Research Article: Co-endemicity of Loiasis and Onchocerciasis in Rain Forest Communities in Southwestern Nigeria

Date Published: March 26, 2015

Publisher: Public Library of Science

Author(s): Olusola Ojurongbe, Akeem Abiodun Akindele, Monsuru Adebayo Adeleke, Matthew Oyebode Oyedeji, Samuel Adeyinka Adedokun, Josephine Folashade Ojo, Callistus Adewale Akinleye, Oloyede Samuel Bolaji, Olusegun Adelowo Adefioye, Oluwaseyi Adegboyega Adeyeba, Jeremiah M. Ngondi.

Abstract: BackgroundLoiasis is currently receiving attention as a disease of public health importance because of the possibility of increased risk of developing neurologic serious adverse event following mass ivermectin treatment against onchocerciasis in individual co-infected with Onchocerca volvulus and Loa loa.Methodology/Principal FindingsRapid assessment procedure for loiasis (RAPLOA) was conducted in 12 communities covering the 3 senatorial districts of Osun State, Nigeria. A total of 960 people were interviewed for history of eye worm using the WHO guidelines for rapid assessment. The survey confirmed the presence of loiasis in all the 12 communities with 4 in Osun East/Ife south senatorial district being at high risk with a prevalence of over 40%. Based on the RAPLOA results, communities within Osun East/Ife south senatorial district were selected for microfilaraemic assessment of L. loa and O. volvulus. A total of 1115 and 1091 individuals were screened for L. loa and O. volvulus microfilaria worms respectively. 160 (14.3%) had L. loa microfilaria detected in their blood with 8 (5.0%) individuals having L. loa loads above 8000 mf/ml. 166 (15.2%) subjects had O. volvulus microfilaria (range 4-504 mf/ml) detected in their skin snip. 30 (2.69%) subjects were co-infected with both L. loa and O. volvulus. There was a significant variation in the prevalence (2.1% to 33.3%) of onchocerciasis in the communities studied (p = 0.001). Five (41.7%) of the studied communities had a prevalence that is equal to or greater than 20%.Conclusions/SignificanceLow prevalence of onchocerciasis and loiasis co-infection in this study suggests that loiasis may not pose a serious epidemiological threat to the continuous distribution and sustainability of ivermectin for the treatment of onchocerciasis. Evaluation of the interruption of onchocerciasis transmissions in this region using all the indicators set forth by WHO is therefore suggested.

Partial Text: Onchocerciasis and loiasis are endemic filarial parasites in the central and western African countries [1] including Nigeria. Onchocerciasis is rated as the second leading infectious cause of blindness in the world only preceded by blinding trachoma [2,3]. It is endemic in 31 countries in Africa, the Arabian Peninsula and 6 in the Americas. 30 out of 36 endemic countries are in sub-Sahara African countries where approximately 99% of all those infected live [2]. Nigeria probably has the highest burden of onchocerciasis in the world, accounting for about a third of the global prevalence [4,5]. The disease has had a major impact on the economic and social lives of the endemic communities [6]. Loiasis, has recently emerged as a disease of public health importance, not because of its own clinical manifestations only but also because of the concern about neurological complications that may occur when ivermectin is given as part of mass treatment programmes for onchocerciasis to people co-infected with Onchocerca volvulus and Loa loa [7]. It is an African disease restricted to the equatorial rain forest regions of Central and West Africa. L. loa is often referred to as the African eye worm because the adult worm can sometimes be seen moving through the sclera of the eye [8].

A total number of 960 people were interviewed for their history of eye worm. Table 1 gives the number of communities surveyed, the number of individuals examined and the percentage of communities that exceeded the thresholds of 40% for RAPLOA. The surveys confirmed the presence of loiasis in all the twelve communities, however, only four communities were high risk communities where over 40% of those interviewed reported a history of eye worm. Osun East senatorial district recorded the highest number of people with history of eye worm.

For over 15 years, free mass treatment with ivermectin has been provided for the control of onchocerciasis and Osun State has been one of the beneficiary States in Nigeria. The community directed distribution of annual doses of ivermectin, coordinated by APOC is now moving from control to eradication phase in many endemic communities. One factor that has been slowing down the control of onchocerciasis in some endemic communities is serious adverse events (SAEs) in individuals with high L. loa microfilaraemia after ivermectin treatment [19][12]. Information on prevalence of loiasis and associated morbidities in onchocerciasis endemic areas therefore remains an important component needed for successful onchocerciasis elimination programme.



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